Hard drive questions

Is there anything special I need to know about SCSI hard drives before I buy one? I know that I need to limit the size to less than 18 or 20gb, but besides that, will any SCSI hard drive work? I found a bunch on eBay but I didn't wanna buy something that's not compatable with my 2000xl. Any info here would be great.

Peace1

Always by scsi or scsi2 hard drive. 50 Pins in the back of the HD.

Thanks for the info. Is that because the MPC has the 50 pin? 'Cause couldn't I just get an adapter cable like I have for my zip. Is there a tech reason for this, like a 50 to 25 pin cable doesn't transfer data well, and it'll work better if its 50 to 50? Also, besides that, is there anything else I need to know, or will any 50pin SCSI, less than 20gb harddrive work